As I didn't find a satisfactory solution to record screencasts, I decided to write a small script tailored to my needs, which were:

stable solution, not crashing 50% of the time

ability to select the window to record

ability to pause and restart recording the same area of the desktop

ability to record sound during the capture

work with Free/Open Source Software

That's not too much asked I guess.... Anyway, here's the solution: screencaster.rb
, a 55 line ruby script using ffmpeg.

When you start, it asks you to click on the window you want to record and what's the directory name (place in /tmp) in which to store the movie(s). It then starts right away recording that region of your desktop. In the terminal where you launched screencast.rb, type p followed by Enter to pause the recording. Then to restart recording, type n followed by Enter (it records each part in separate files). To quit, enter q+Enter.

I've used it to record a screencast, and it worked flawlessly. To produce the final file, I used .Kdenlive